This invention relates to an improved composition for Fourdrinier fiberboard and additionally to an improvement in the Fourdrinier process of fabrication.
Fiberboard has a wide application, for example, as acoustical ceiling tile. For this purpose, it has particularly good sound attenuating properties and has an attractive appearance. In addition to acoustical applications, fiberboard is also typically employed for heat insulating and flame barriers, wall panels, and the like.
Fiberboard is normally manufactured in accordance with one of two basic fabrication techniques. One process, known as the cast method, involves essentially essentially blending a fibrous material with a heavy bodied starch-water paste, casting or spreading the mixture out in slab form, and subsequently kiln drying. The other manufacturing method, to which this invention particularly relates, is known as the Fourdrinier process.
The general Fourdrinier technique as referred to herein involves the use of a Fourdrinier or cylinder screen machine of the type generally found in the paper manufacturing industry, or similar equipment having the purpose of extracting water from a fiber slurry such as under vacuum. Applying such Fourdrinier method, a relatively thin slurry comprising water, starch binder and mineral fiber, with flocculent sometimes added, is felted onto the screen machine, most of the water is withdrawn, and the sheet is then heat dried. The heat gelatinizes the starch into the adhesive in situ, thus forming what is generally referred to as "felted" board.
Although various starchy materials can be used as binder, a highly desirably one from various viewpoints has been tapicoa starch since, among other factors, it has a low gelatinization temperature and gives a rapid increase in viscosity after gelatinization temperature is reached. This rapid increase in viscosity, or in other words, this ability of the starch to paste quickly is conductive to effective bonding. Tapioca starch is, however, an imported product and is subject to fluctuation in supply, quality, uniformity and cost.
One object of this invention is to provide a fiberboard composition adapted for the Fourdrinier process using other than unmodified tapioca starch as a binder and which possesses satisfactory sag and strength properties.
Another object of this invention is to provide a Fourdrinier fiberboard composition in which the binder has little or no tendency to migrate.
Still another object of the invention is to provide a Fourdrinier fiberboard composition containing a starch binder having a low gelatinization temperature.
An additional object of the invention is to provide a Fourdrinier fiberboard composition containing a starch binder which reaches its maximum aqueous viscosity at a relatively low temperature.
Yet another object of the invention is to provide a Fourdrinier fiberboard composition containing a starch binder having a relatively high maximum viscosity.
A further object of the invention is to provide an improvement in the Fourdrinier machine process for making fiberboard through which a much better dispersion of the binder in the board is achieved with attendant increases in strength and related properties.
Yet a further object of the invention is to provide an improvement in the Fourdrinier machine process for making fiberboard whereby starches much lower in purity than heretofore thought suitable can now be satisfactorily employed.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.